From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
To: Dima Stepanov <dimastep@yandex-team.ru>
Cc: fam@euphon.net, kwolf@redhat.com, yc-core@yandex-team.ru,
qemu-block@nongnu.org, "Michael S. Tsirkin" <mst@redhat.com>,
Jason Wang <jasowang@redhat.com>,
qemu-devel@nongnu.org, raphael.norwitz@nutanix.com,
arei.gonglei@huawei.com, fengli@smartx.com, stefanha@redhat.com,
marcandre.lureau@redhat.com, pbonzini@redhat.com,
mreitz@redhat.com
Subject: Re: [PATCH v2 5/5] vhost: add device started check in migration set log
Date: Tue, 19 May 2020 11:24:22 +0100 [thread overview]
Message-ID: <20200519102422.GC2798@work-vm> (raw)
In-Reply-To: <20200519090735.GA17826@dimastep-nix>
* Dima Stepanov (dimastep@yandex-team.ru) wrote:
> On Mon, May 18, 2020 at 10:53:59AM +0100, Dr. David Alan Gilbert wrote:
> > * Dima Stepanov (dimastep@yandex-team.ru) wrote:
> > > On Mon, May 18, 2020 at 10:50:39AM +0800, Jason Wang wrote:
> > > >
> > > > On 2020/5/16 上午12:54, Dima Stepanov wrote:
> > > > >On Thu, May 14, 2020 at 03:34:24PM +0800, Jason Wang wrote:
> > > > >>On 2020/5/13 下午5:47, Dima Stepanov wrote:
> > > > >>>>> case CHR_EVENT_CLOSED:
> > > > >>>>> /* a close event may happen during a read/write, but vhost
> > > > >>>>> * code assumes the vhost_dev remains setup, so delay the
> > > > >>>>> * stop & clear to idle.
> > > > >>>>> * FIXME: better handle failure in vhost code, remove bh
> > > > >>>>> */
> > > > >>>>> if (s->watch) {
> > > > >>>>> AioContext *ctx = qemu_get_current_aio_context();
> > > > >>>>>
> > > > >>>>> g_source_remove(s->watch);
> > > > >>>>> s->watch = 0;
> > > > >>>>> qemu_chr_fe_set_handlers(&s->chr, NULL, NULL, NULL, NULL,
> > > > >>>>> NULL, NULL, false);
> > > > >>>>>
> > > > >>>>> aio_bh_schedule_oneshot(ctx, chr_closed_bh, opaque);
> > > > >>>>> }
> > > > >>>>> break;
> > > > >>>>>
> > > > >>>>>I think it's time we dropped the FIXME and moved the handling to common
> > > > >>>>>code. Jason? Marc-André?
> > > > >>>>I agree. Just to confirm, do you prefer bh or doing changes like what is
> > > > >>>>done in this series? It looks to me bh can have more easier codes.
> > > > >>>Could it be a good idea just to make disconnect in the char device but
> > > > >>>postphone clean up in the vhost-user-blk (or any other vhost-user
> > > > >>>device) itself? So we are moving the postphone logic and decision from
> > > > >>>the char device to vhost-user device. One of the idea i have is as
> > > > >>>follows:
> > > > >>> - Put ourself in the INITIALIZATION state
> > > > >>> - Start these vhost-user "handshake" commands
> > > > >>> - If we got a disconnect error, perform disconnect, but don't clean up
> > > > >>> device (it will be clean up on the roll back). I can be done by
> > > > >>> checking the state in vhost_user_..._disconnect routine or smth like it
> > > > >>
> > > > >>Any issue you saw just using the aio bh as Michael posted above.
> > > > >>
> > > > >>Then we don't need to deal with the silent vhost_dev_stop() and we will have
> > > > >>codes that is much more easier to understand.
> > > > >I've implemented this solution inside
> > > > >hw/block/vhost-user-blk.c:vhost_user_blk_event() in the similar way by
> > > > >using the s->connected field. Looks good and more correct fix ). I have
> > > > >two questions here before i'll rework the fixes:
> > > > >1. Is it okay to make the similar fix inside vhost_user_blk_event() or
> > > > >we are looking for more generic vhost-user solution? What do you think?
> > > >
> > > >
> > > > I think I agree with Michael, it's better to have a generic vhost-user
> > > > solution. But if it turns out to be not easy, we can start from fixing
> > > > vhost-user-blk.
> > > I also agree, but as i see it right now the connect/disconnect events
> > > are handled inside each vhost-user device implementation file. So it will
> > > need some global refactoring. So i suggest having this fix first and
> > > after it refactoring the code:
> > > - more devices will be involved
> > > - i see there is some difference in device handling
> >
> > I'm following bits of this discussion, some thoughts;
> > if your device doesn't support reconnect, then if, at the start of
> > migration you find that you can't start the log what is the correct
> > behaviour?
> I'm not sure here, but it looks like that in this case the device state
> will be:
> disconnect -> stopped (will not be changed during migration, because
> reconnect isn't supported)
> And because of it the device state will not be changed during migration,
> so there is no need for log and migration could be completed
> successfully.
> So as i see it (i could be wrong here) that:
> - it is okay: if device is not started and we will not change this
> state during migration + log start is failed
> - it is not okay: if device is started + log start is failed (because
> we can't handle the dirty pages and so on during migration)
Yes, that does make sense to me.
> > You can't carry on with the migration because you'd have an
> > inconsistent migration state; so I guess that's why the abort() is there
> > - but I think I'd generally prefer to fail the migration and hope the
> > vhsot device is still working for anything other than the log.
> >
> > You're going to have to be pretty careful with the ordering of reconect
> > - reconnecting on the source during a migration sounds pretty hairy, but
> > a migration can take many minutes, so if you really want to survive this
> > I guess you have to.
> Maybe if we get a disconnect during migration then we could postphone or
> just don't make reconnect at all till the end of migration on the source
> side. This will make a device left in the stopped state.
Yes, that's the easiest way, but you may find people object to it being
out for that long.
Dave
> Thanks, Dima.
>
> >
> > Dave
> >
> >
> > > >
> > > >
> > > > >2. For migration we require an additional information that for the
> > > > >vhost-user device it isn't an error, because i'm trigerring the
> > > > >following assert error:
> > > > > Core was generated by `x86_64-softmmu/qemu-system-x86_64 -nodefaults -no-user-config -M q35,sata=false'.
> > > > > Program terminated with signal SIGABRT, Aborted.
> > > > > #0 0x00007fb56e729428 in raise () from /lib/x86_64-linux-gnu/libc.so.6
> > > > > [Current thread is 1 (Thread 0x7fb486ef5700 (LWP 527734))]
> > > > >
> > > > > (gdb) bt
> > > > > #0 0x00007fb56e729428 in raise () from /lib/x86_64-linux-gnu/libc.so.6
> > > > > #1 0x00007fb56e72b02a in abort () from /lib/x86_64-linux-gnu/libc.so.6
> > > > > #2 0x00005648ea376ee6 in vhost_log_global_start
> > > > > (listener=0x5648ece4eb08) at ./hw/virtio/vhost.c:857
> > > > > #3 0x00005648ea2dde7e in memory_global_dirty_log_start ()
> > > > > at ./memory.c:2611
> > > > > #4 0x00005648ea2e68e7 in ram_init_bitmaps (rs=0x7fb4740008c0)
> > > > > at ./migration/ram.c:2305
> > > > > #5 0x00005648ea2e698b in ram_init_all (rsp=0x5648eb1f0f20 <ram_state>)
> > > > > at ./migration/ram.c:2323
> > > > > #6 0x00005648ea2e6cc5 in ram_save_setup (f=0x5648ec609e00,
> > > > > opaque=0x5648eb1f0f20 <ram_state>)
> > > > > at ./migration/ram.c:2436
> > > > > #7 0x00005648ea67b7d3 in qemu_savevm_state_setup (f=0x5648ec609e00) at
> > > > > migration/savevm.c:1176
> > > > > #8 0x00005648ea674511 in migration_thread (opaque=0x5648ec031ff0) at
> > > > > migration/migration.c:3416
> > > > > #9 0x00005648ea85d65d in qemu_thread_start (args=0x5648ec6057f0) at
> > > > > util/qemu-thread-posix.c:519
> > > > > #10 0x00007fb56eac56ba in start_thread () from
> > > > > /lib/x86_64-linux-gnu/libpthread.so.0
> > > > > #11 0x00007fb56e7fb41d in clone () from /lib/x86_64-linux-gnu/libc.so.6
> > > > > (gdb) frame 2
> > > > > #2 0x00005648ea376ee6 in vhost_log_global_start
> > > > > (listener=0x5648ece4eb08) at ./hw/virtio/vhost.c:857
> > > > > 857 abort();
> > > > > (gdb) list
> > > > > 852 {
> > > > > 853 int r;
> > > > > 854
> > > > > 855 r = vhost_migration_log(listener, true);
> > > > > 856 if (r < 0) {
> > > > > 857 abort();
> > > > > 858 }
> > > > > 859 }
> > > > > 860
> > > > > 861 static void vhost_log_global_stop(MemoryListener *listener)
> > > > >Since bh postphone the clean up, we can't use the ->started field.
> > > > >Do we have any mechanism to get the device type/state in the common
> > > > >vhost_migration_log() routine? So for example for the vhost-user/disconnect
> > > > >device we will be able to return 0. Or should we implement it and introduce
> > > > >it in this patch set?
> > > >
> > > >
> > > > This requires more thought, I will reply in Feng's mail.
> > > Okay, let's continue discussion there.
> > >
> > > No other comments mixed in below.
> > >
> > > Thanks, Dima.
> > >
> > > >
> > > > Thanks
> > > >
> > > >
> > > > >
> > > > >Thanks, Dima.
> > > > >
> > > > >>Thank
> > > > >>
> > > > >>
> > > > >>> - vhost-user command returns error back to the _start() routine
> > > > >>> - Rollback in one place in the start() routine, by calling this
> > > > >>> postphoned clean up for the disconnect
> > > > >>>
> > > >
> > >
> > --
> > Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
> >
>
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
next prev parent reply other threads:[~2020-05-19 10:25 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-30 13:36 [PATCH v2 0/5] vhost-user reconnect issues during vhost initialization Dima Stepanov
2020-04-30 13:36 ` [PATCH v2 1/5] char-socket: return -1 in case of disconnect during tcp_chr_write Dima Stepanov
2020-05-06 8:54 ` Li Feng
2020-05-06 9:46 ` Marc-André Lureau
2020-04-30 13:36 ` [PATCH v2 2/5] vhost: introduce wrappers to set guest notifiers for virtio device Dima Stepanov
2020-05-04 0:36 ` Raphael Norwitz
2020-05-06 8:54 ` Dima Stepanov
2020-05-11 3:03 ` Jason Wang
2020-05-11 8:55 ` Dima Stepanov
2020-04-30 13:36 ` [PATCH v2 3/5] vhost-user-blk: add mechanism to track the guest notifiers init state Dima Stepanov
2020-05-04 1:06 ` Raphael Norwitz
2020-05-06 8:51 ` Dima Stepanov
2020-04-30 13:36 ` [PATCH v2 4/5] vhost: check vring address before calling unmap Dima Stepanov
2020-05-04 1:13 ` Raphael Norwitz
2020-05-11 3:05 ` Jason Wang
2020-05-11 9:11 ` Dima Stepanov
2020-05-12 3:26 ` Jason Wang
2020-05-12 9:08 ` Dima Stepanov
2020-05-13 3:00 ` Jason Wang
2020-05-13 9:36 ` Dima Stepanov
2020-05-14 7:28 ` Jason Wang
2020-04-30 13:36 ` [PATCH v2 5/5] vhost: add device started check in migration set log Dima Stepanov
2020-05-06 22:08 ` Raphael Norwitz
2020-05-07 7:15 ` Michael S. Tsirkin
2020-05-07 15:35 ` Dima Stepanov
2020-05-11 0:03 ` Raphael Norwitz
2020-05-11 9:43 ` Dima Stepanov
2020-05-11 3:15 ` Jason Wang
2020-05-11 9:25 ` Dima Stepanov
2020-05-12 3:32 ` Jason Wang
2020-05-12 3:47 ` Li Feng
2020-05-12 9:23 ` Dima Stepanov
2020-05-12 9:35 ` Dima Stepanov
2020-05-13 3:20 ` Jason Wang
2020-05-13 9:39 ` Dima Stepanov
2020-05-13 4:15 ` Michael S. Tsirkin
2020-05-13 5:56 ` Jason Wang
2020-05-13 9:47 ` Dima Stepanov
2020-05-14 7:34 ` Jason Wang
2020-05-15 16:54 ` Dima Stepanov
2020-05-16 3:20 ` Li Feng
2020-05-18 2:52 ` Jason Wang
2020-05-18 9:33 ` Dima Stepanov
2020-05-18 9:27 ` Dima Stepanov
2020-05-18 2:50 ` Jason Wang
2020-05-18 9:41 ` Dima Stepanov
2020-05-18 9:53 ` Dr. David Alan Gilbert
2020-05-19 9:07 ` Dima Stepanov
2020-05-19 10:24 ` Dr. David Alan Gilbert [this message]
2020-05-19 9:59 ` Michael S. Tsirkin
2020-05-19 9:13 ` Dima Stepanov
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